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ROLE OF DOM PHOTOREACTIONS IN CONTROLLING UV EXPOSURE OF CORAL ASSEMBLAGES IN THE FLORIDA KEYS
Citation:
Zepp, R G., E. Davis, S. L. Anderson, D L. Santavy, L J. Hansen, AND K. Patterson. ROLE OF DOM PHOTOREACTIONS IN CONTROLLING UV EXPOSURE OF CORAL ASSEMBLAGES IN THE FLORIDA KEYS. Presented at The International Chemical Congress of Pacific Basin Societies, Honolulu, HI, December 14-19, 2000.
Impact/Purpose:
The overall objective of this task is to develop quantitative relationships for assessing the vulnerability of aquatic resources to global change. The task will contribute experimental and modeling tools for assessments of the interactions of global climate and UV changes with coral reefs and selected watersheds and estuaries in the U.S. These activities are contributing primarily to two APGs in the ecosystems component of the Global Change Research Multiyear Plan: the 2006 APG (APG 3) on building the capacity to assess global change impacts on coastal aquatic ecosystems, including coral reefs and estuaries and the 2004 APG (APG 2) on building capacity to assess and respond to global change impacts on selected watersheds. One major task objective is to assess interactions of global warming and UV exposure that are contributing to the observed coral bleaching and disease. Our lab is working with scientists at the NHEERL Gulf Ecology Lab to characterize UV exposure and effects at several coral reef sites. Other research in this task is examining the interactions between UV-induced breakdown of refractory organic matter in estuaries and coastal areas that enhance UV penetration into the water and concurrently form biologically-labile nitrogen-, phosphorus- and carbon-containing substances that stimulate productivity and microbial activity. This task also involves research in central Brazil that is part of the Large Scale Biosphere Atmosphere Experiment (LBA). The objectives of this project are to assess the impacts of land use and climatic changes on soil nutrient cycles and microbiota, trace gas exchange and water quality in the Brazilian cerrado. This work involves a close collaboration between EPA and a group of scientists from the Department of Ecology, University of Brasilia, Brazil. Other objectives of this task are to assess the interactions of land use and climate changes with the ecological functioning of streams in watersheds of the Piedmont region of the southestern U.S.
Description:
Recent studies have indicated that solar LTV radiation is a significant stressor of coral assemblages in tropical and subtropical marine environments. Here evidence is presented that UV exposure of coral reefs in the Florida Keys near Key West is controlled by the colored component of dissolved organic matter, referred to as CDOM, in waters overlying the reefs. Downwelling and upwelling vertical profiles of LTV and visible radiation were obtained and absorption and fluorescence spectra of the filtered water samples were measured. Analyses of the absorption spectral data indicated that they could be closely described by a non-linear exponential function, a(lambda) = a(412)* exp b(412 - lambda), where b ranged from 0.022 up to 0.025. The CDOM photobleached with loss of LTV absorbance and fluorescence when exposed to simulated solar radiation. These results indicate that interactions between photobleaching and transport of the CDOM out over the reefs likely control UV penetration to the reef surface.